1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of the Related Art
Image forming apparatuses designed to form images with toner by means of electrophotography, electrostatic recording, or otherwise find application in copying machines, printers, facsimile machines, and so forth for general purpose use. As an electrophotographic image forming apparatus, for example, there has heretofore been known the one composed of: a photoreceptor having formed on its surface a photosensitive layer; a charging section for electrifying the surface of the photoreceptor; an exposure section for applying signal light to the surface of the photoreceptor in a charged state whereby to form an electrostatic latent image corresponding to predetermined image data; a developing section for supplying toner to the electrostatic latent image on the surface of the photoreceptor whereby to change (develop) the electrostatic latent image into a toner image; a transfer section for transferring the toner image on the surface of the photoreceptor onto a recording medium; a fixing section for fixing the toner image transferred on the recording medium into place; and a cleaning section for removing residual toner remaining on the surface of the photoreceptor following the completion of the transference of the toner image on the recording medium. In such an electrophotographic image forming apparatus, its fixing section is designed to achieve fixation of a toner image by melting the toner constituting the toner image, and therefore a heat fixing method is generally adopted for heating the toner image at a high temperature. However, the heat fixing method necessitates heating section such as a heater that is high in power consumption to effect heating, which results in an undesirable increase in the quantity of power consumed. Thus, in the light of environmental issues such as global warming, extensive research and study have been made in an effort to achieve a reduction in power consumption. As an example of fixing methods that consume less power, there has been known a wet fixing method that is in no need of a heating section such as a heater. According to the wet fixing method, a fixing fluid which produces the effect of swelling and softening toner is applied to a toner image to swell and soften the toner constituting the toner image. In this way, the toner image can be fixed onto a recording medium. More specifically, for example, in an image forming apparatus designed to perform image formation by using a method involving a step of transferring a toner image formed on a surface of a photoreceptor onto an intermediary transfer medium such as an intermediary transfer belt and a step of transferring and fixing the toner image formed on the intermediary transfer medium onto a recording medium, before the toner image formed on the intermediary transfer medium is fixed onto the recording medium, a fixing fluid is applied to the toner image to swell and soften the toner constituting the toner image.
There has also been known a fixing fluid coating apparatus composed of a fixing fluid chamber for storing a fixing fluid in which is housed a coating roller which is used to apply the fixing fluid to an unfixed toner image formed on an intermediary transfer medium in a contact manner (for example, refer to Japanese Unexamined Patent Publication JP-A 2004-333866). Moreover, shown in FIG. 8B related to JP-A 2004-333866 is a sponge roller as an example of the coating roller for applying the fixing fluid to the unfixed toner image in a contact manner. The sponge roller has an axially disposed path for the fixing fluid. In the sponge roller, the fixing fluid externally supplied to the fixing fluid path is allowed to permeate through its surface, so that the fixing fluid can be applied to the unfixed toner image in a contact manner. That is, the coating roller disclosed in JP-A 2004-333866 is made of a material which exhibits liquid permeability and has a space for storing the fixing fluid formed interiorly thereof. In this coating roller, the fixing fluid stored inside exudes to the top surface, so that the exudation of the fixing fluid can be applied to the unfixed toner image in a contact manner. Moreover, as described in paragraphs [0050] to [0051] of JP-A2004-333866 with reference to FIG. 9, there is proposed a fixing fluid coating apparatus that includes, in addition to the fixing fluid chamber and the coating roller, an excessive fixing fluid recovery portion for collecting an excess of the fixing fluid remaining on a recording medium. The excessive fixing fluid recovery portion is designed in the form of a cartridge so as to be freely replaceable. That is, according to JP-A 2004-333866, part of the components constituting the fixing fluid coating apparatus is designed in the form of a cartridge so as to be freely attachable to and detachable from a main body of an image forming apparatus.
The sponge roller disclosed in JP-A 2004-333866 is composed of a single liquid-permeable material. In this case, however, it is extremely difficult to exercise control over the amount of application of the fixing fluid properly. Therefore, a larger amount of the fixing fluid than is necessary may be applied to a recording medium, which is causative of generation of, for example, wrinkles and curls in the recording medium, especially in the case of using a paper sheet or the like as the recording medium. Another problem is an undesirable increase in fixing fluid consumption. Furthermore, in the fixing fluid coating section disclosed in JP-A 2004-333866, the sponge roller is disposed vertically below the fixing fluid chamber. In this construction, it is inevitable that, as the sponge roller is rotated, so its surface is squeezed at the location where the sponge roller and the fixing fluid chamber make contact with each other, thus causing the fixing fluid to leak outside. As a result, the constituent components disposed inside the image forming apparatus are contaminated with a leakage fixing fluid, which leads to shortening of the service life of the image forming apparatus. Thus, this construction not only necessitates an additional upkeep operation to remove a leakage fixing fluid but also gives rise to a possibility of further augmentation of the amount of the fixing fluid to be consumed. In addition, because of its less-than-satisfactory long-term durability, the sponge roller is in need of replacement over the course of time. However, JP-A 2004-333866 pays no regard to the section for replacing the sponge roller at all. This could lead to impairment of the long-term durability of the image forming apparatus.
Moreover, in the sponge roller disclosed in JP-A 2004-333866, the fixing fluid is supplied to the fixing fluid path through a feeder formed in the rotary shaft of the roller so as to communicate with the fixing fluid path. However, JP-A 2004-333866 provides no specific description about how the fixing fluid is externally supplied to the rotary shaft. That is, it is difficult in reality to implement the sponge roller thus constructed. Let it be assumed that the front end of the rotary shaft of the sponge roller has a section connected thereto, for supplying the fixing fluid from external. In this case, since the rotary shaft is designed to rotate every time image formation is effected, it follows that the connection suffers from a durability disadvantage, wherefore the fixing fluid may leak from the connection to a bearing portion that will eventually cause contamination of the interior of the image forming apparatus. Furthermore, in the fixing fluid coating apparatus disclosed in JP-A 2004-333866, only the excessive fixing recovery portion is designed in the form of a cartridge. In this case, two upkeep operations, namely replenishment of the fixing fluid and discard of an excess of the fixing fluid need to be carried out on an individual basis, which results in deterioration in ease of handling of the image forming apparatus as a whole.